In a multiplayer game, if Player A's unit moves to a battlefield, then Player A moves that unit out with an action during the open showdown, then Player B's unit moves in with an action, then Player C's unit moves in with an action, is this legal and who becomes the attacker?

Ruling: The situation is legal. After Player A leaves, the battlefield is no longer in a Pending Combat state, so both Player B and Player C can legally move in. Based on current rules, both B and C would technically be defenders, though this outcome seems unintended and will likely be clarified in future rules updates.

Sequence:

• Player A's unit moves to battlefield
• Player A moves their unit out with an action (battlefield no longer has Pending Combat)
• Player B's unit moves in with an action
• Player C's unit moves in with an action

Nuances:

• Rule 623.1 only prevents moves to battlefields with Pending Combats or Combats in Progress by players who don't already have permanents there
• Once Player A leaves, it stops being a Pending Combat (which requires units from two opposing players)
• The current rules create an ambiguous situation where both B and C would be defenders, which is likely not intended
• This area of the rules is expected to be clarified in future updates